1. Field of the Invention
The present invention relates to a developing apparatus and an image forming apparatus comprising this developing apparatus and a storage apparatus to be used in an image forming process of an electrophotographic system.
2. Related Background Art
Heretofore, in general, in an image forming apparatus using an image forming process of an electrophotographic system, as a developing apparatus which develops an electrostatic latent image formed on a photosensitive member by a developer (toner), the developing apparatus using a non-magnetic toner has been known.
In such a developing apparatus, a configuration has been widely adopted, in which a developing roller which is a toner bearing member which bears a toner, and a removing supply roller (hereinafter referred to as RS roller) which is a member that supplies the toner on the surface of this developing roller or removing the toner on the surface of the developing roller or performing both removing and supplying are provided, and this RS roller is disposed so as to abut against the developing roller.
Citing one example of the RS roller, there is a roller consisting of a sponge layer and a cored bar, which rotates in a counter direction for a developing roller with a predetermined peripheral velocity. The developing roller and the RS roller are abutted against each other with a predetermined pushed-in amount, whereby the toner of the developing roller is removed, and the toner is supplied to the developing roller.
Here, the above described pushed-in amount is a value showing how far an outer diameter (virtual outer diameter) of the RS roller pushes into the outer diameter of the developing roller, which can be found by a value subtracting a center distance between the developing roller and the RS roller from the sum of the radius of the developing roller and the radius of the RS roller.
In the meantime, it has been well known that, by unitizing the developing apparatus and making it detachably attachable to an image forming apparatus main body, the improvement of maintainability can be attempted.
In such a developing apparatus, a method has been proposed, in which an operational status of the developing apparatus is detected, thereby an abutting pressure of the RS roller is changed, so that the deterioration of the toner due to an excessive toner removal capability is prevented under high temperature environment (for example, see Japanese Patent Application Laid-Open No. H9-211957).
Further, a method has been proposed, in which, to prevent a permanent deformation of the RS roller in a long term storage of the developing apparatus, the RS roller is isolated from the developing roller when the developing apparatus is detached from the image forming apparatus main body, and accompanied with an operation to mount the developing apparatus onto the image forming apparatus main body, the developing roller and the RS roller are pressured (for example, see Japanese Utility Model Publication No. H4-30599).
Further, a method has been proposed, in which the RS roller is biased to the developing roller by biasing means, and in timing with the case where the RS roller is hardened due to permanence (toner clogging), the pushed-in amount of the RS roller is decreased (for example, see Japanese Patent Application Laid-Open No. 2003-122121).
Now, in recent years, a tendency toward high image quality has been advancing in the image forming apparatus of an electrophotographic system, and it has become of a crucial importance to properly adjust a removal capability of the RS roller for the developing roller and a supply capability of the toner to realize a high image quality. In the meantime, the RS roller has been suffering from irregularities of initial characteristics such as the toner removal capability and the toner supply capability of the RS roller due to a difference (maker difference) by a plurality of maker's plants and a plurality of makers, and a lot difference.
To restrain these irregularities, it has been necessary to make a production process complicated, or to tolerate these irregularities, it has been necessary to control, for example, the pushed-in amount of the RS roller for the developing roller with a high accuracy.
Furthermore, there has been a problem in that the RS roller gradually changes in the characteristics such as the toner removal capability and the toner supply capability due to elapse-time usage, and this change in the characteristics hinders a long life of the developing apparatus or the image quality ends up fluctuating in correspondence with the change in the characteristics.
Further, as described above, the RS roller rotates in a counter direction to the developing roller, and moreover, abuts against the developing roller with a predetermined pushed-in amount. Consequently, when the developing roller and the RS roller are rotationally driven, a load applied on the surface of the RS roller becomes extremely large, and in an initial usage stage, a tearing has often occurred in the RS roller due to this load. Hence, at the production time of the developing apparatus, a process of coating the toner in advance on the RS roller has been added, thereby preventing the tearing from occurring with the toner used as a lubricant.
Furthermore, there has been a problem that a starting torque when the developing roller and the RS roller are simultaneously driven in the developing apparatus is extremely large since the RS roller rotates in a counter direction for the developing roller, and abuts against the developing roller with a predetermined pushed-in amount, and by this difference of the starting torque due to the difference of characteristic, the rotation of the RS roller has ended up fluctuating, so that the image quality has often been fluctuated.